1. Field of the Invention
The invention relates to a caulked retaining member, one end of which is bent through a calking process to form a caulked portion, that holds a member along a base of the caulked retaining member through the clamping force of the caulked portion, a method for retaining a member by caulking, a structure of a caulked retaining member, and a caulking apparatus for a caulking process.
2. Description of the Related Art
There is known a rotation-translation conversion actuator that is mounted in an internal combustion engine or the like to apply a translational driving force to the engine (e.g., see Japanese Patent Application Publication No. 2007-303408 (JP-A-2007-303408) and Japanese Patent Application Publication No. 2007-303479 (JP-A-2007-303479)). The publications, JP-A-2007-303408 and JP-A-2007-303479 each describe a rotation-translation conversion actuator that drives a valve lift device of an internal combustion engine. A rotary body is rotatably supported in the main body case of the rotation-translation conversion actuator via a bearing. The rotary body is rotationally driven by a motor. Thus, a screw shaft makes a translational movement in an axial direction to drive the valve lift device.
In JP-A-2007-303408 and JP-A-2007-303479, an annular support member is arranged inside the housing and bolted to an inner surface of the housing to fix the bearing for rotatably supporting the rotary body in the housing.
However, due to the configuration in which the annular support member is arranged inside the housing and fastened by the bolt to fix the bearing as described above, the housing tends to be large. In order to prevent the housing from increasing in size, a method of supporting the bearing through a caulking process instead of using the annular support member or bolting the annular support member.
However, if the housing is simply caulked and the bearing is clamped in the housing in the case where a member requiring a certain clamping force, such as the bearing or the like, is held by the housing, the residual axial force of the housing as a force serving to generate the clamping force cannot be sufficiently increased. As a result, the clamping force for holding the bearing may become insufficient. In order to increase the residual axial force, it is conceivable to apply a pressure to a base of a work in the same direction as the direction of the clamping force apart from a position where the work is bent through the caulking process.
However, in the caulking process for the bearing as described above, the rotational resistance of the bearing needs to be held small. For this purpose, the application of the pressure for increasing the residual axial force needs to be prevented from increasing in the radial strain of the bearing.
As a caulking process for other purposes, there are known an art in which the inflexion point of a change rate of a pressure exerted by an electric press is set as a completion point of the press operation (see Japanese Patent Application Publication No. 2001-162396 (JP-A-2001-162396)) and an art in which an inflexion point corresponding to a decrease in the caulking load of a caulking punch is detected based on the relationship between the caulking load and a caulking stroke of the caulking punch to control the amount of a material with which a groove is filled (see Japanese Patent Application Publication No. 2002-35864 (JP-A-2002-35864)).
In addition, conventionally a groove is formed between a caulking portion of a workpiece and a contour region of the workpiece to prevent a caulking process from affecting the contour of the work (see Japanese Patent Application Publication No. 2005-34857 (JP-A-2005-34857)). Further, there are known an art in which a load is applied to a bearing side to increase the clamping force resulting from caulking (see Japanese Patent Application Publication No. 2008-223840 (JP-A-2008-223840)), and an art in which a spherical bearing is fixed to a housing by tumbling one of both sides separated from each other by a V-shaped groove (see Japanese Patent Application Publication No. 2002-21867 (JP-A-2002-21867)).
If a configuration is adopted in which a held member, such as a bearing or the like, is held by a caulked portion by applying pressure to the base of a workpiece in the same direction as the direction of a clamping force without applying pressure to the caulking portion, it is conceivable to further combine with this caulking process the method in which the inflexion point of the pressurization force is set as the completion point of the press operation as described in JP-A-2001-162396. However, even if this method is combined with the caulking process, it is unclear whether the member such as the bearing or the like may be restrained from being radially strained as the method described in JP-A-2001-162396 is put into practice in the caulking process.
This also holds true where the art of the caulking punch described in JP-A-2002-35864 is applied. It is unclear whether the member such as the bearing or the like is restrained from being radially strained through the caulking punching.
Furthermore, in JP-A-2005-34857, JP-A-2008-223840, and JP-A-2002-21867, when caulking part of the workpiece onto the member such as the bearing or the like, no consideration is given to the idea of restraining the member from being radially strained.